selinux: add a skb_owned_by() hook

Commit 90ba9b1986b5ac (tcp: tcp_make_synack() can use alloc_skb())
broke certain SELinux/NetLabel configurations by no longer correctly
assigning the sock to the outgoing SYNACK packet.

Cost of atomic operations on the LISTEN socket is quite big,
and we would like it to happen only if really needed.

This patch introduces a new security_ops->skb_owned_by() method,
that is a void operation unless selinux is active.

Reported-by: Miroslav Vadkerti <mvadkert@redhat.com>
Diagnosed-by: Paul Moore <pmoore@redhat.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: linux-security-module@vger.kernel.org
Acked-by: James Morris <james.l.morris@oracle.com>
Tested-by: Paul Moore <pmoore@redhat.com>
Acked-by: Paul Moore <pmoore@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/security.h

@@ -1638,6 +1638,7 @@ struct security_operations {
 	int (*tun_dev_attach_queue) (void *security);
 	int (*tun_dev_attach) (struct sock *sk, void *security);
 	int (*tun_dev_open) (void *security);
+	void (*skb_owned_by) (struct sk_buff *skb, struct sock *sk);
 #endif	/* CONFIG_SECURITY_NETWORK */
 
 #ifdef CONFIG_SECURITY_NETWORK_XFRM
@@ -2588,6 +2589,8 @@ int security_tun_dev_attach_queue(void *security);
 int security_tun_dev_attach(struct sock *sk, void *security);
 int security_tun_dev_open(void *security);
 
+void security_skb_owned_by(struct sk_buff *skb, struct sock *sk);
+
 #else	/* CONFIG_SECURITY_NETWORK */
 static inline int security_unix_stream_connect(struct sock *sock,
 					       struct sock *other,
@@ -2779,6 +2782,11 @@ static inline int security_tun_dev_open(void *security)
 {
 	return 0;
 }
+
+static inline void security_skb_owned_by(struct sk_buff *skb, struct sock *sk)
+{
+}
+
 #endif	/* CONFIG_SECURITY_NETWORK */
 
 #ifdef CONFIG_SECURITY_NETWORK_XFRM

net/ipv4/tcp_output.c

@@ -2709,6 +2709,7 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
 	skb_reserve(skb, MAX_TCP_HEADER);
 
 	skb_dst_set(skb, dst);
+	security_skb_owned_by(skb, sk);
 
 	mss = dst_metric_advmss(dst);
 	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)

security/capability.c

@@ -737,6 +737,11 @@ static int cap_tun_dev_open(void *security)
 {
 	return 0;
 }
+
+static void cap_skb_owned_by(struct sk_buff *skb, struct sock *sk)
+{
+}
+
 #endif	/* CONFIG_SECURITY_NETWORK */
 
 #ifdef CONFIG_SECURITY_NETWORK_XFRM
@@ -1071,6 +1076,7 @@ void __init security_fixup_ops(struct security_operations *ops)
 	set_to_cap_if_null(ops, tun_dev_open);
 	set_to_cap_if_null(ops, tun_dev_attach_queue);
 	set_to_cap_if_null(ops, tun_dev_attach);
+	set_to_cap_if_null(ops, skb_owned_by);
 #endif	/* CONFIG_SECURITY_NETWORK */
 #ifdef CONFIG_SECURITY_NETWORK_XFRM
 	set_to_cap_if_null(ops, xfrm_policy_alloc_security);

security/security.c

@@ -1290,6 +1290,11 @@ int security_tun_dev_open(void *security)
 }
 EXPORT_SYMBOL(security_tun_dev_open);
 
+void security_skb_owned_by(struct sk_buff *skb, struct sock *sk)
+{
+	security_ops->skb_owned_by(skb, sk);
+}
+
 #endif	/* CONFIG_SECURITY_NETWORK */
 
 #ifdef CONFIG_SECURITY_NETWORK_XFRM

security/selinux/hooks.c

@@ -51,6 +51,7 @@
 #include <linux/tty.h>
 #include <net/icmp.h>
 #include <net/ip.h>		/* for local_port_range[] */
+#include <net/sock.h>
 #include <net/tcp.h>		/* struct or_callable used in sock_rcv_skb */
 #include <net/net_namespace.h>
 #include <net/netlabel.h>
@@ -4363,6 +4364,11 @@ static void selinux_inet_conn_established(struct sock *sk, struct sk_buff *skb)
 	selinux_skb_peerlbl_sid(skb, family, &sksec->peer_sid);
 }
 
+static void selinux_skb_owned_by(struct sk_buff *skb, struct sock *sk)
+{
+	skb_set_owner_w(skb, sk);
+}
+
 static int selinux_secmark_relabel_packet(u32 sid)
 {
 	const struct task_security_struct *__tsec;
@@ -5664,6 +5670,7 @@ static struct security_operations selinux_ops = {
 	.tun_dev_attach_queue =		selinux_tun_dev_attach_queue,
 	.tun_dev_attach =		selinux_tun_dev_attach,
 	.tun_dev_open =			selinux_tun_dev_open,
+	.skb_owned_by =			selinux_skb_owned_by,
 
 #ifdef CONFIG_SECURITY_NETWORK_XFRM
 	.xfrm_policy_alloc_security =	selinux_xfrm_policy_alloc,